Purpose Ipilimumab is a T-cell-potentiating monoclonal antibody directed against cytotoxic T-lymphocyte antigen-4 (CTLA-4) to promote antitumoural immunity. In phase III trials, ipilimumab was shown to be the first agent to improve survival in advanced melanoma patients, regardless of previous treatment. We report a case of severe neurologic disease after ipilimumab treatment. Patient and methods Neurologic symptoms including facial diplegia, tetraplegia, areflexia progressed with time a few days after the fourth monthly ipilimumab infusion. Analysis of the cerebro-spinal fluid showed elevated proteinorachy and lymphocytic meningitis. Despite high doses of steroids and symptomatic treatment, the symptoms worsened. Results Veinoglobulins were then infused and the patient began to improve and recovered almost normal activity two years later. Conclusion The adverse event profile associated with ipilimumab was primarily immune-related. This is the first case in which such a severe event has been reported.